The balanced equation is
4Fe(s) + 3O2(g) ---> 2Fe2O3(s)
here four moles of Fe will react with O2 to give 2 moles of Fe2O3
mass of Fe reacted = 33.4 grams
moles of Fe reacted = mass of Fe / atomic mass of Fe
moles of Fe reacted = 33.4 / 55.8 = 0.599 moles
moles of Fe2O3 formed = 0.5 X 0.599 = 0.2995 moles
so mass of Fe2O3 formed = moles X molar mass = 0.2995 X 159.69 = 47.83 g